The present invention relates to a power supply device, and in particular to a power supply device for exciting a converter transformer by switching a primary input thereto, thereby obtaining a high-voltage output at the secondary side thereof.
In certain apparatus such as a copying machine or a laser beam printer, there are required a high-voltage power supply for a charger for charging a photosensitive member, and another power supply for obtaining a DC-overlapped AC developing bias voltage for controlling the developing condition of a developing unit.
In such apparatus there is generally employed a method of converting the commerical line supply voltage to a lower voltage in the order of 24 V for stabilization, and elevating the voltage again, followed by rectification, in a high-voltage power supply unit.
In the conventional apparatus the aforementioned high-voltage DC power supply for the charger and the other power supply for obtaining the DC-overlapped AC output for the developing bias voltage are constructed as separate units, and both are designed to obtain desired voltages by elevating a low voltage. Particularly the DC and AC voltages for the developing unit have been obtained with separate converters, so that the power supply unit is complex in structure and cannot be easily compactized.